Depending on what kinds of trees you have, you may get no fruit at all. Some fruit trees are "self-fruitful," meaning they don't require pollination from a different tree to bear fruit, but that doesn't sound like the case in your situation. Even for trees that are self-fruitful, yields are often increased if another variety is planted nearby for cross-pollination. If another variety of fruit tree of the same species is within 500 feet or so of yours, and you have bees and other insects in the neighborhood, they will likely take care of the pollination for you. If your neighbors have some of the same kinds of fruit trees, you may not need to plant a pollinator. However, if the trees are not planted close together, or if insect pollinators are lacking, you may not get good yields. It won't work to just plant another tree of the same variety, either. For cross-pollination to happen, the trees must be genetically different from each other (but still the same species). For example, pollen from a 'Fuji' apple won't pollinate another Fuji apple, but it would pollinate a 'Gala' apple. And it's impossible for an apple tree to pollinate a pear, cherry, peach, or plum.